Fusing stations for both black and white and color reproduction apparatus (electrophotographic copier/printers or the like) are well known. In view of the large number of copies required in today's businesses, higher speed reproduction apparatus are required. Typically in the lower speed reproduction apparatus, internal heaters have been used with the fuser rollers. A cushion layer that is typically more insulative than thermally conductive in nature has been used around an inner core of the roller.
It has been found that with high-speed reproduction apparatus, i.e., copy speeds of over 100 copies per minute, it is difficult to transfer the heat to the fuser roller at a rate effective to perform the fusing operation and it is difficult to supply the heat uniformly as the fusing operation proceeds. In other words, the heat removed from the roller to the substrate bearing the image to be fused is taken from the surface of the heater at a point referred to as a “nip” between the fuser roller and a pressure roller. It is difficult to maintain a uniform level of heat on the exterior of the fuser roller with the heat being removed at a variable rate in the nip.
Similar difficulties have been encountered with external heater rollers, which are typically anodized aluminum rollers, that are heated and in contact with the fuser roller. A primary difficulty is that the materials used heretofore to form the fuser roller have typically not been selected to have the thermal properties required to transfer the greater quantities of heat required and to permit transfer of the heat within the fuser rollers to maintain temperature uniformity consistent with long-term service with the roller and consistent with the thermal conductivities of many existing roller structures.
Accordingly a continuing search has been directed to the development of an improved fuser roller and an improved fusing system to ensure efficient heat transfer both into the fuser roller and through the layers of the fuser roller.